How to call folders in file explorer

Hi Brian
 
I hope you are doing well.
I have question for you. I would like to create a drop down list for lots of folders in a folder (these folders are not in the project folder or directory).
Suppse we have a folder in our computer and in that folder we have 35 folders. So these 35 folder should be in the drop down list in the dialog box (instead of writing the folders name in my dialog box, I would like to pick the name from the list)
Is it possible to do that?
I have attached the dialog box I created
 
That would be great if you could help me
 
Thanks,